Crew members set the stage at the North Charleston Coliseum, Wednesday, Jan. 13, 2016, in North Charleston, S.C., in advance of Thursday's Fox Business Network Republican presidential debate. (AP Photo/Rainier Ehrhardt)

NORTH CHARLESTON, S.C. (AP) — A smaller cast of Republican presidential candidates takes the debate stage Thursday night, with Ted Cruz under new scrutiny for a big loan from Goldman Sachs and Donald Trump labeled by his main rival as embodying "New York values."

The prime-time showdown in South Carolina will highlight a race that has cleaved into two distinct — and increasingly heated — contests, with time dwindling to sway voters before the Feb. 1 Iowa caucuses.

The debate comes after the revelation that Cruz failed to disclose on federal campaign fundraising reports some $1 million in loans used to help finance his 2012 Senate run. The funds included money from Goldman Sachs, the investment banking firm where his wife, Heidi Cruz, serves as a managing director.

The Texas senator's campaign called failure to report the loans "a mistake." Cruz had previously said that he and his wife liquidated "our entire net worth" to finance his underdog Senate bid.

After months of civility toward Cruz, front-runner Trump is now targeting the Texan.

"I know nothing about it, but I hear it's a very big thing," Trump said of the loan in an interview with Bloomberg Politics posted online Thursday. "I think he's a nice guy, and I hope he gets it solved."

Trump is also suggesting the Canadian-born senator may be challenged by Democrats as ineligible to be president.

Cruz dismisses that claim and is returning the fire, accusing the brash businessman of having "New York values" and questioning his foreign policy credentials.

While those two anti-establishment candidates battle each other, four other candidates are fighting to become the more mainstream Republican alternative.

Florida Sen. Marco Rubio is seen by some as having a slim edge in that group, opening him to criticism from his rivals about his immigration views as well as the 44-year-old's youth and relative inexperience.

The divide between the anti-Washington and establishment candidates has given definition to a race that has been otherwise unwieldy and chaotic. Trump has led for months in national polls.

Former Florida Gov. Jeb Bush has been among the few establishment Republicans jabbing Trump in recent weeks. In a likely preview of his debate tactics, Bush sharply criticized Trump on Wednesday for holding positions on taxes, guns and health care that he said were out of step with conservatives.

"He's not a conservative," Bush said. "For a conservative party we need to elect a conservative. For us to fix the mess in Washington, D.C., we have to apply conservative principles."

For Thursday night's debate, host Fox Business Network tightened the qualifying rules, resulting in the smallest group of candidates in the headline event to date. Also on the main stage will be New Jersey Gov. Chris Christie and Ohio Gov. John Kasich, who are battling Rubio and Bush for the establishment vote, as well as retired neurosurgeon Ben Carson, whose standing in the race has steadily fallen.

Christie is enjoying a burst of support in New Hampshire, where he's devoted significant time to courting the state's blend of moderate and libertarian voters. He's had strong debate performances in the past and is likely to face heightened scrutiny from his rivals as a result of his rise in the first-in-the-nation primary state.

The debate rules resulted in businesswoman Carly Fiorina being bumped to the undercard event. Kentucky Sen. Rand Paul was also demoted, but is choosing not to participate in the early evening contest.

To qualify for the main debate, a candidate had to place in the top six in an average of recent national polls, or in the top five in an average of recent Iowa or New Hampshire polls.

Republicans have one more debate scheduled before voting begins in Iowa, a Jan. 28 event in Des Moines.

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